The present invention relates to a device for dispensing of a powdered drug preparation by inhalation. The device is in particular a multiple-dose device without propellant gas, equipped with a metering means, which dispenses doses from a powder container. The device of the invention is useful, for example, in the treatment of asthma.
The administering of a powdered drug preparation by inhalation from an inhaler is known. Multidose type powder inhalers comprising a drug container and a metering member for measuring and dispensing a unit dose are also known, for example from patent publications GB 2165159, EP 79478, and EP 166294. In these devices, a series of dosing recesses are notched into the surface of a cylindrical metering member, and the said member is disposed in a chamber of precisely the same shape. When the metering member is rotated, the dosing recesses in turn will move first to a position in alignment with the powder container for being filled and thereafter to a position in alignment with the inhalation channel, whereupon a unit dose will fall by gravity from the dosing recess into the inhalation channel. Thereafter the dose of medicament is inhaled from the inhalation channel. These devices have the drawback that they make overdosing of the medicament possible by allowing the dispensing of a plurality of doses in succession into the inhalation channel, whereby a multiple dose may be drawn by one inhalation.
Attempts have been made to solve the above-mentioned problem by using dispensing systems in which the dosing recess will not be emptied into the inhalation channel by gravity but, instead, the dose of medicament is inhaled directly from the dosing recess, such recesses having been notched into the surface of a metering member having the shape of a cylinder, a cone or a truncated cone, as disclosed in patent publications WO 92/00771 and WO 92/09322. Also in these devices, a metering member having the shape of a cylinder, a cone or a truncated cone is disposed in a chamber having precisely the same shape. When the metering member is rotated, the dosing recesses will move first to a position in alignment with the flow container for filling, and then to the inhalation channel, which is shaped so that the dosing recess will be emptied under the effect of the air flow being inhaled, and thereafter, having rotated through a full 360°, back to a position in alignment with the flow container. Since the metering member is, for purposes of metering precision, disposed within a chamber of the same shape, and since it has to be rotated through 360°, the metering member may be prone to jamming as powder falls onto the surfaces of the device.
The above problem is at least partly avoided in multidose powder inhalers having a metering member in the form of a slide or a rod movable in its longitudinal direction. Such devices have been described e.g. in patent publications EP 758911 B, WO 97/17097, U.S. Pat. No. 5,447,151, U.S. Pat. No. 5,263,475, U.S. Pat. No. 5,765,552 and WO 92/18188. The metering rod or slide equipped with a dosing recess may extend through the interior of the medicament container or it may slide below the orifice of the medicament container.
The above devices have a drawback that they are sensitive to external moisture, which can have a detrimental effect on the measuring accuracy of the device. If a powdered medicament is moistened, e.g. during storage or use of the device, it may form lumps which results in incomplete filling of the dosing recess. Furthermore, if the internal surfaces which are in contact with the discharging medicament powder, e.g. the metering member and the air channel, become moist, the amount of the medicament can be reduced to a fraction of the normal. The moistening may be a result of e.g. an exhalation through an inhaler. For keeping the device free of moisture or dirt, the devices usually have a protective cover, which must be opened before use.